1. Field of the Invention
The present invention relates to a wafer flattening process for locally etching projecting portions on the surface of a wafer by an activated species gas to flatten the same or locally etching relatively thick portions of the wafer to make the distribution of thickness of the wafer uniform and to a storage medium for the same.
2. Description of the Related Art
FIG. 9 is a schematic sectional view of an example of a wafer flattening process of the related art.
In FIG. 9, reference numeral 100 is a plasma generator. The plasma generator 100 sprays the activated species gas G generated in the plasma from a nozzle 101 to the surface of the wafer W.
The wafer W is placed on and affixed to a stage 120. The stage 120 is made to move in the horizontal direction so as to guide the portion Wa relatively thicker than the prescribed thickness on the surface of the wafer W (hereinafter referred to as the xe2x80x9crelatively thick portionxe2x80x9d) directly under the nozzle 101.
The activated species gas G is sprayed from the nozzle 101 to the projecting relatively thick portion Wa to locally etch the relatively thick portion Wa and make the distribution of thickness of the surface of the wafer W uniform.
The thickness of the relatively thick portion Wa of the wafer W however is also not uniform, but is diverse.
Therefore, technology has been devised for controlling the relative speed,of the nozzle 101 with respect to the wafer W in accordance with the thickness of the relatively thick portion Wa (for example, the technology described in Japanese Patent Laid-Open No. 9-2 7482).
This technology calls for the positions and thicknesses of the relatively thick portions Wa to be measured over the entire surface of the wafer W by a wafer flatness measuring device and for two-dimensional data of the positions and thicknesses to be prepared. The data is then converted to position-relative speed data showing the positions of the relatively thick portions Wa and the relative speed of the nozzle 101 by which the relatively thick portions Wa become the desired flatness after etching.
Next, the stage 120 is controlled based on this position-relative speed data to move the nozzle directly above the predetermined relatively thick portions Wa to etch the entire surface of the wafer W.
That is, at locations of relatively thick portions Wa with large thicknesses, the relative speed of the nozzle 101 is slowed to increase the amount of etching, while at locations of relatively thick portions Wa with small thicknesses, the relative speed of the nozzle 101 is increased to reduce the amount of etching, whereby the entire surface of the wafer W is flattened.
In the above wafer flattening process of the related art, however, there were the following problems.
FIG. 10 is a view of the state of spraying of the activated species gas G from the nozzle 101, FIG. 11 is a schematic view for explaining the flattening operation by superposition of the activated species gas G, and FIG. 12 is a schematic sectional view for explaining the problem in the wafer flattening process of the related art.
As shown in FIG. 10, the activated species gas G sprayed from the nozzle 101 spreads out as it heads downward. The portion of the wafer W directly beneath the nozzle 101 is therefore etched deeply, while the portions away from that are etched shallowly.
Accordingly, while the nozzle 101 is scanning the surface, as shown in FIG. 11, the area Wb of the wafer W starts to be etched by the activated species gas G sprayed from the nozzle 101 then heading toward the area Wb.
For example, assuming that the nozzle 101 moves from the left to the right in FIG. 11 and that the edge of the outskirt of the activated species gas G sprayed from the nozzle 101 reaching the position Q1 of the etching radius r from the left end of the area Wb contacts the edge of the area Wb, the area Wb is etched by the activated species gas G from the nozzle 101 moving from the position Q1 toward the position Q2 and is not affected by the activated species gas G at the pont of time when the nozzle 101 reaches the position Q2.
That is, the area Wb is etched by the superposition of the activated species gas G of the nozzle 101 moving between the positions Q1 to Q2. At this time, when the relatively thick portion of the area Wb is thick, the relative speed of the nozzle 101 moving between the positions Q1 and Q2 becomes slower in accordance with that thickness, while when the relatively thick portion of the area Wb is thin, the relative speed becomes faster, whereby the area Wb is etched flat.
With this wafer flattening process, however, there was the problem that the outer rim of the wafer W ended up being left thick.
That is, as shown in FIG. 12, when the nozzle 101 scans from the outside to the inside of the outer rim Wc, the nozzle 101 is moved at a high speed at the outside of the outer rim Wc and changes in relative speed in accordance with the thickness of the outer rim Wc when it reaches the position of the outer rim Wc, so the outer rim Wc is not affected much at all by the activated species gas G of the nozzle 101 when moving from the left. Therefore, when the outer rim is not the above relatively thick portion, there is not that much of a problem with the flattening of the outer rim, but when the outer rim is a relatively thick portion, the amount of etching of the outer rim is halved, the desired amount of etching is not achieved, and, as shown in FIG. 12, the area near the outer rim Wc ends up becoming remarkably thick compared with the inside portion of the wafer W.
The present invention was made to solve the above problems and has as its object to provide a wafer flattening process designed to flatten the entire surface of the wafer including the outer rim of the wafer by inserting dummy data corresponding to the data of the outer rim of the wafer in the data of the outside of the wafer and to provide a storage medium for the same.
To achieve the above object, according to a first aspect of the present invention, there is provided a wafer flattening process which causes a nozzle to scan the entire surface of a wafer based on position-speed data comprised of coordinates on a plane including the surface of the wafer and a nozzle relative speed set substantially inversely proportionally to the value of thickness of the wafer at those coordinates and flattens the wafer by activated species gas sprayed from the nozzle, the wafer flattening process comprising the steps of: using, as dummy data, position-speed data outside of a predetermined area set on the wafer closest to an imaginary line extending from the center of the wafer in the radial direction; and setting the nozzle relative speed of the dummy data to be substantially the same as the nozzle relative speed of the position-speed data of the outer rim of the above predetermined area and on the imaginary line.
Due to this configuration, when a nozzle is made to scan the entire surface of the wafer based on the position-speed data, the relative speed of the nozzle changes in a state substantially inversely proportional to the values of the thickness of the different portions of the wafer. At this time, since the nozzle, when at a position outside of the predetermined area closest to the imaginary line, scans the surface at substantially the same speed as the nozzle relative speed of the position-speed data at the outer rim of the predetermined area on the imaginary line due to the dummy data, the outer rim is etched like if by the activated species gas of the nozzle heading from the predetermined area along the imaginary line at the identical speed.
Depending on the wafer, it may be sufficient to flatten only a certain area in the inside at a high precision and may be not necessary to flatten the entire surface of the wafer at a high precision.
Therefore, in a preferred embodiment of the first aspect of the invention, the above predetermined area is a flatness quality area set at the inside of the wafer.
Alternatively, in another preferred embodiment of the first aspect of the invention, the above predetermined area is the entire area of the surface of the wafer.
Further, in a preferred embodiment of the first aspect of the invention and its embodiments, the dummy data exists only within a distance of about half of the etching diameter of the activated species gas from the outer rim of the predetermined area.
Due to this configuration, the nozzle relative speed becomes substantially the same as the nozzle relative speed set for the predetermined area only when the nozzle located at the outside of the predetermined area moves within a distance of about half of the etching diameter of the activated species gas from the outer rim of the predetermined area.
Note that the invention may also cover a storage medium storing the above position-speed data.
Therefore, according to a second aspect of the present invention, there is provided a storage medium storing position-speed data comprised of coordinates on a plane including the surface of the wafer and a nozzle relative speed set substantially inversely proportionally to the value of thickness of the wafer at those coordinates, wherein position-speed data outside of a predetermined area set on the wafer closest to an imaginary line extending from the center of the wafer in the radial direction is used as dummy data and the nozzle relative speed of the dummy data is set to be substantially the same as the nozzle relative speed of the position-speed data of the outer rim of the above predetermined area on the imaginary line.
In a preferred embodiment of the second aspect of the invention, the above predetermined area is a flatness quality area set at the inside of the wafer. Alternatively, the above predetermined area is the entire area of the surface of the wafer. Further, preferably the dummy data exists only within a distance of about half of the etching diameter of the activated species gas from the outer rim of the predetermined area.